The Speed of Light in Your Kitchen Visiting the Local Hot Spots (page 2)

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Author: Jerry Silver

Expected Results

Suppose you find the average of the hot-spot distance is 6 cm.

The wavelength of the microwave resonant in the microwave oven is 12 cm.

In meters, this is 12 cm × 0.01 m/cm × 0.12 m.

The speed of light is then, c = 0.12m × 2,450,000,000Hz = 2.94 × 108 m/s.

This is reasonably close to the accepted value, which is just under 3 × 108 m/s (300,000,000 m/s). Remember, microwaves may vary in how they create standing waves and an error factor is associated with heat distribution on the heat surface. For this reason, this measurement can be only expected to give ballpark, not precisely accurate, values.

Why It Works

A microwave oven produces a resonant wave in the oven chamber similar to that of a vibrating guitar string. The hot spots are like the nodes or the points where the ends of the string are held. A complete wave is a cycle up and down, so only a half wave fits between the two nodes in both cases. From knowing the frequency of the microwaves and measuring its wavelength, we can find the speed of light.

Other Things to Try

A more sophisticated, but more precise way to measure the speed of light is to detect the interference between light waves separated by a measurable distance. Equipment to do this is available from scientific supply vendors, such as PASCO.

The Point

The speed of a wave, such as light, can be determined from its wavelength and frequency. The wavelength of a microwave oven can be found by the distance between the nodes of a resonant standing wave.

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